Origin of nodular lymphocyte-predominant Hodgkin's disease from a clonal expansion of highly mutated germinal-center B cells.

The atypical cells of nodular lymphocyte-predominant Hodgkin's disease, designated lymphocytic and histiocytic (L&H) cells, have a B-cell phenotype. To clarify the clonality of these cells, we studied rearranged immunoglobulin genes for the variable region of the heavy chain (V[H] genes) in individual L&H cells from 11 patients with nodular lymphocyte-predominant Hodgkin's disease. We also studied the expression of immunoglobulin light chains by those cells in six of the same patients. Single CD20+ L&H cells were isolated from frozen sections by a technique of micromanipulation. The rearranged V(H) genes of these cells were amplified by the polymerase chain reaction (PCR), sequenced, and compared with germ-line V(H) genes. Immunoglobulin light-chain messenger RNA (mRNA) was detected by in situ hybridization. Of 615 L&H cells isolated from all the frozen sections, 160 yielded PCR products. In each of the 11 patients, the L&H cells that could be evaluated had identically rearranged V(H) genes, whether they were isolated from the same nodule, different nodules, or different blocks of tissue. All the V(H) sequences derived from the L&H cells were highly mutated (7.5 to 27.2 percent). In two cases the coding capacity of the V(H) genes was completely or partially disrupted by mutations. Intraclonal diversity was found in six cases, and monotypic immunoglobulin light-chain mRNA was found in six. The L&H cells of nodular lymphocyte-predominant Hodgkin's disease represent a monoclonal expansion of B cells. The high load of V(H) gene mutations and signs of intraclonal diversity suggest a relation between L&H cells and germinal-center B cells at the centroblastic stage of differentiation.